Manufacturing of integrated circuits (ICs) typically involves performing numerous processes on a wafer. For example, the processes can include polishing, deposition, photolithography, etching, cleaning, heat treatment as well as other processes. These processes are generally performed on different processing tools. In addition, different products may require different set of processes or recipes. It is not uncommon for a wafer to pass through over 400 processing steps during manufacturing.
The wafers are processed in lots. A container such as a cassette stores one or more lot(s) of wafers. Conventional cassettes store up to 25 wafers. A cassette is loaded into a carrier, such as standard mechanical interface (SMIF) or front opening unified pod (FOUP) for transport throughout the factory. One or more production lots are carried by a carrier to undergo a fabrication task. When a production lot is introduced into the production line, it is usually associated with a carrier. During processing, wafers can be dropped off due to, for example, exceptions encountered in the line. The dropped-off wafers are subsequently scrapped.
Improved handling of lots in a manufacturing process is desirable to increase production efficiency and throughput.